The invention relates to a method for securing data stored in the memory of a portable data medium as well as a system for securing such data.
Portable data media are used for storing various data. Such data media serve, for example, for storing medical data of persons and recently data media have also been used for storing data representing amounts of money or other value units. This last type of data medium is also referred to as an electronic wallet. The data media represent a value corresponding to the amount of money or value units stored therein, which, in the event the data medium is lost or stolen, represents a loss to the rightful owner. It is, on the other hand, conceivable that a deceitful owner changes data on the data medium in order to pretend the availability of greater amounts and thus to defraud the user's bank or the card issuer. It is also possible that with fraudulent claims for damages of supposedly lost data media, a greater amount of money than that still stored in the data media can be claimed. Furthermore, in the case of other types of data media the loss or unauthorized change of data can have unpleasant or even serious consequences.